The design embodiment of such an incubator with respect to the air guidance is an important element, on the one hand, for achieving a uniform temperature on the lying surface with the patient, without generating high flow velocities, and, on the other hand, for still ensuring a stable temperature and humidity of the air in the incubator space with the access opening open, especially due to the front flap being open.
To achieve a uniform air guidance, DE 4008822 A1 provides for allowing the air to rise through air feed openings around the lying surface and for drawing it off via an air return channel with an opening in the vicinity of the incubator hood cover. The air is guided essentially in a closed circuit via a fan or ventilator with a downstream air heater and optionally combined with an air humidifier.
Consequently, it has been known from the state of the art that uniform feed of the generally heated and optionally humidified air is advantageous for the most uniform temperature possible on the lying surface.
However, it was found in all attempts at solving this problem so far that great problems are caused for the air guidance especially by the drawing off of the air. Recirculation is preferred for reasons of energy saving and economical reasons, because the heated air would otherwise be released to the environment via openings in the upper area of the incubator hood and would not be essentially recirculated. The drawn-off, heated and relatively humid air is condensed in the air return channel according to the above state of the art. This leads to contaminations and possibly to microbial contamination. In addition to this drawback, the air return channel may obstruct the view of the medical personnel of the operating and patient monitors through the otherwise generally transparent incubator hood, these monitors often standing or being arranged on the front side of the incubator.
According to another prior-art solution in EP 0162375 A1, the warm air is fed in only on the longitudinal sides of the incubator in parallel to the lying surface and is removed or drawn off on the two front sides in relation to the lying surface.
One drawback of this prior-art solution is that direct short circuits of air are formed at the air channels joining each other in the corners of the incubator hood, so that the heated air does not flow uniformly upward, but is drawn off again into the next exhaust channel. One consequence of this deflection of the air is that the temperature profile is highly nonuniform and the warm air curtain desirable in the area of the longitudinal sides of the lying surface does not function. The temperature drop in the interior space of the incubator may reach up to 5.degree. C. when the front flap is opened on one of the longitudinal sides, which is not acceptable in the case of sensitive and sick premature babies.
According to another possible solution, the air is guided in double walls. However, double walls have the drawback that they have a disturbing effect in hospital practice due to a doubling of the surfaces to be cleaned. Another important drawback is that the air above the lying surface is no longer in direct contact with the ambient air of the incubator. Heating processes take much longer, and it also takes longer to cool the incubator with the patient to a lower temperature.